drivers/analog: fix adc ads1115 driver

[arikimari]

Summary

Fix reg write function so that it works with all platfroms

• platfroms that that does not support I2C_M_NOSTART flag
• function always writes 3 bytes, this implementation is more efficient,
  no need for to two separate i2c messages
  Remove one unused static function (causing compile warning)
  Fix documentation of channels

Impact

Platforms using ads1115 driver from Nuttx

Testing

Custom nxp93 hw with ads1115 adc

Test code:

_ads1115 = ads1115_initialize(imx9_i2cbus_initialize(2),
                                   CONFIG_ADC_ADS1115_ADDR);
if (ads1115 != NULL)
  {
    adc_msg.am_channel = 6;
    adc_msg.am_data = 0;
    ads1115->ad_ops->ao_ioctl(ads1115,ANIOC_ADS1115_READ_CHANNEL,
                                     (long unsigned int)&adc_msg);
    _alert("ads1115 adc channel 6 value: %d\n", adc_msg.am_data);_

Output of this is:

ads1115 adc channel 6 value: 8778

Value is correct for this channel 6 (voltage is so that value should be about 8800)

[acassis]

@arikimari please fix:

❌ Missing git commit message
Used config files:
1: .codespellrc
Some checks failed. For contributing guidelines, see:
https://github.com/apache/nuttx/blob/master/CONTRIBUTING.md
Error: Process completed with exit code 1.

[linguini1]

The change is good, but please provide some information about how you tested and some logs of the results.

[arikimari]

The change is good, but please provide some information about how you tested and some logs of the results.

Test code added and logs from results